1. Field of the Invention
This invention is related to the field of lock mechanisms and, more particularly, to multiple-key lock mechanisms.
2. Description of the Related Art
There are many situations calling for limited access to a home or business, for example, by custodial or repair persons. In many such cases, one-time access may be all that is required. However, giving out a key in these situations grants unlimited entry and therefore compromises security. It would be desirable to have a means of locking a door that would allow one-time access to designated persons, and unlimited access to the owner.
Auto-makers have recognized the usefulness of this concept as applied to automobiles, and a number of currently-manufactured cars are equipped with master and valet keys, which differ in that the valet key provides limited access to the vehicle. For example, the glove compartment and trunk typically cannot be unlocked with the valet key. In some cases, the length of time the engine will operate when started with the valet key is also limited. However, such systems are not directly applicable to building access, where what must be restricted is not the number or type of doors that the valet key can unlock, but rather the number of times it can be used to open them. Furthermore, the access restriction systems used in automobiles are often electronic, and may become non-functional in the event of power loss. This is completely unacceptable in a building security system.
Key lock security systems exist based on master/service keys, which provide different levels of access. For example, a master key might allow a hotel manager to enter any of the rooms in a hotel, while the service key issued to a tenant permits entry only to the tenant""s own room. U.S. Pat. No. 2,422,600 to Swanson, for instance, describes such a system. U.S. Pat. No. 4,631,941 to Sjunnesson (hereinafter, Sjunnesson) illustrates another variant of this idea. Sjunnesson describes a door lock that may be set in either a normal lock or a service lock position, depending on whether the occupant wishes to allow access by service personnel in his absence. The service key provided to janitorial staff in a hotel, for example, would work to unlock only those doors that had been left in the service lock position, thus restricting access. Neither of these simple master/service key arrangements, however, provides the advantage of limiting the service key to one-time access.
The problems outlined above are in large part solved by a master/valet keyset and lock as described herein. The mechanism comprises a lock that may be locked in either a master or a valet mode. Furthermore, the lock may be opened with either a master key or a valet key. These keys provide different levels of access. Using the master key, the lock can be locked and unlocked any number of times. Furthermore, when the lock has been locked in the master mode only the master key can be used to unlock it. When locked in the valet mode, the lock can be unlocked only once using the valet key. After it has been opened with the valet key and subsequently relocked, it can only be unlocked again by the master key. This system provides a means whereby the owner of the master key can permit one-time access to the building to an individual possessing a valet key, for example, a maintenance person. After the individual has entered the building using their valet key and relocked the door, only the master key will unlock the door again. Thus, if the valet key were to be lost or stolen it could not be improperly used to gain entry.
The master/valet keyset and lock may further comprise a turnstile system and a barrier pin. The turnstile system allows a valet key to turn in only one direction and the barrier pin prevents the valet key from rotating the lock from the valet locked position to the master locked position. Thus, a lock left in the valet lock position can be turned once to the unlocked position, and once more to the master locked position. At this point, the valet key is incapable of unlocking the door a second time; only the master key can restore the lock to the valet locked position. By this means, one-time access is provided to the holder of the valet key.
A method is also contemplated for locking a door in either a master mode or valet mode and for providing two types of keys, corresponding to these modes. The method further involves the use of a master key that can unlock the door and can lock it in either the master or the valet mode, and a valet key that can only lock the door in the master mode and can only unlock the door if it is locked in the valet mode.
It is considered advantageous to have the capability to lock a door in a limited access mode, whereby authorized individuals are allowed one-time access. This capability might serve well, for example, when it was necessary to enter an office after hours once each week, say, to collect waste paper for recycling. The individual performing this service would be issued a valet key, and on the day the collection service was to be performed the office door would be locked in the valet mode. Using the valet key, the office could be entered just once and relocked after collecting the papers. The valet key would not allow entry at any other time. Thus, even if the key were lost or stolen, the security of the office would not be seriously compromised.